Gpss (General Purpose Simulation System)

A package to simulate discrete event system. A Client-server system. A general queuing system. Developed by Jeff Gordon of IBM around 1961, 1962.
GPSS is not a programming system like Simscript; one doesn’t “write” program here, but design a network of Blocks through which percolating simulation objects collectively alludes to a sense of process.

A discrete event simulator that basically sees system dynamics via change of states of queues, storages, facilities (servers), switch, etc.

Another possibility

The clients (processes) are called transactions. GPSS is a transaction-based simulation system.

The program is a collection of steps (or blocks) which do something. Minimally
GENERATE

Generates transactions

On a timeline, they would appear as

As these transactions percolate through blocks, the system state changes by their behavior. Ultimately each transaction would be

terminated as they hit the TERMINATION block.
An example of a single queuing system follows.
Client-server1.gps
10 generate 12,8 ; transactions generated

Every server is called a Facility. The facility used here is CPU. It served 251 transactions (customers). Its utilization rate is very low, only 66.7%. Therefore, idle time: 23.3%

Average time spent by a transaction is 7.99 units. No transaction retried to get the server.

Maximum queue count was 2. At the time simulation ended, queue count was 1. 175 out of 251 transactions found the queue empty. Average time spent in the queue is 0.975, average count of the queue is 0.081. Average time spent in the queue by those who entered a non-empty queue is 3.219.